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Session 21 - Luminous Infrared Galaxies.
Display session, Wednesday, January 07
Exhibit Hall,

[21.08] Massive stars near and far: Investigating the stellar populations of starbursts with ISO-SWS Spectroscopy

M. D. Thornley, D. Lutz, H. W. W. Spoon, D. Kunze (MPE), A. Sternberg (Tel Aviv U.), T. Alexander, F. Bertoldi (MPE)

We report on recent starburst modeling results which utilize Short Wavelength Spectrometer (SWS) observations of a large sample of sources, taken as part of the MPE GTO proposal on Bright Galactic Nuclei. This project aims to produce a general model for starbursts which is consistent with the observed properties of nearby star-forming regions as well as those of the nuclei of more distant starburst galaxies. We use this model to determine the population of massive stars needed to produce the observed mid-infrared line emission.

Our model of a large-scale starburst consists of individual "delta-burst" superclusters, the properties of which are convolved with a chosen star formation history in order to produce the global properties of the starburst. The observed infrared line ratios for our starburst sample suggests that starburst nuclei produce very massive stars, up to at least 50 M_ødot, for a range of star formation histories. Such an upper mass cutoff is significantly higher than that inferred by recent studies of near-infrared line ratios.

To examine the validity of the model "delta-burst" components, we compare the model properties with those of nearby star-forming regions. At present, we are concentrating on two nearby regions: the dust-obscured Galactic H II region W51 IRS2 and the "mini-starburst" 30 Doradus in the LMC. The observed infrared line ratios indicate that both regions are fairly young (ages < 6 Myr), short bursts, with upper mass cutoffs of \ge50-100 M_ødot, consistent with the properties of their model counterparts.

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